Jake Hyde will be out for four to six weeks with an ankle ligament injury.
The forward had a scan on Thursday to assess the full extent of an injury picked up in training on Sunday.
The scan revealed significant damage to his ankle ligaments and soft tissue but was ultimately promising with the 23-year-old likely to return before the end of the year.
Hyde is currently the Bees’ second top goalscorer but the blow has been somewhat softened by the return of Spanish forward Dani Lopez.
Lopez scored four times in five games during a brief loan spell last season and he is available to face Wrexham on Sunday.